Position sensor for electromagnetic actuator to detect a position of a shaft

ABSTRACT

A position sensor includes a shaft to be detected, a first magnet being fixed to the shaft and having a first polarity vector parallel to an axis of the shaft, a second magnet being disposed opposite to the first magnet and having a second polarity vector crossing the first polarity vector substantially orthogonally three-dimensionally, and first and second semiconductor magnetoresistive elements being disposed over the second magnet and functioning as a magnetoelectric transducer having a magnetosensitive axis substantially orthogonal to the first and second polarity vectors. The first and second elements generate an output responsive to an axial movement of the shaft.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION NO. PCT/JP01/06729.

TECHNICAL FIELD

The present invention relates to a position sensor for anelectromagnetic actuator which is used in various systems for a vehicleand detects a position of a shaft to be detected which moves axially insynchronization with a movable shaft of the electromagnetic actuator.

BACKGROUND ART

To meet recently-increasing requirement for improving fuel efficiency ofa vehicle, various measures directed toward the improvement of the fuelefficiency have been studied. Among them, a high voltage of a batteryenables an electromagnetic actuator such as a linear solenoid or thelike to have both a great driving force and miniaturization.Consequently, the electromagnetic actuator, which having a higherefficiency to various kinds of electronics systems than a mechanicalactuator, has been studied. In order to apply the electromagneticactuator to these electronics systems, the position of a movable shaftmust be controlled accurately. Accordingly, a position sensor becomesimportant for the accurate position detection of the movable shaft.

With reference to FIG. 7, a conventional position sensor (disclosed inJapanese Patent Laid-Open No. 5-264326) for the electromagnetic actuatorwill be hereinafter described.

FIG. 7(a) is a perspective general view of the conventional positionsensor for the electromagnetic actuator.

FIG. 7(b) shows a cross section taken along arrow C—C of the sensor.

FIG. 7(c) is a perspective view detailing a relationship between amagnetoelectric transducer and a magnetic field generator of the sensor.

In FIGS. 7(a), 7(b) and 7(c), reference numeral 100 denotes a shaft tobe detected. Reference numeral 100 a denotes a guide groove formed in alongitudinal direction of the shaft 100. Reference numeral 110 denotes amagnet 110 polarized magnetically in a thickness direction. Referencenumeral 120 denotes a magnetic plate made of a permalloy shaped like anisosceles triangle. Reference numeral 130 denotes a magnetic fieldgenerator including the magnet 110 and the magnetic plate 120 attachedtogether in their respective longitudinal direction matching together.Reference numeral 140 denotes a magnetoelectric transducer. Referencenumeral 310 denotes a flat surface of the shaft 100. Reference numeral320 denotes a slider including an insulating material engages with theguide groove 100 a, for sliding smoothly relative to the shaft 100. Themagnetoelectric transducer 140 provided at the slider 320 is mounted inparallel with the magnetic field generator 130 provided on the flatsurface 310 of the shaft 100.

An operation of the conventional sensor will be explained below.

The shaft 100 is displaced relative to the slider 320 (in the directionof an arrow D in FIG. 7(a)), the magnetic plate 120 is opposed to themagnetoelectric transducer 140 accordingly with various widths.Consequently, an electric field sensed by the magnetoelectric transducer140 varies in strength accordingly, thus enabling the sensor to detectthe position of the shaft 100.

The conventional position sensor described above, however, has thefollowing problem. The conventional position sensor for theelectromagnetic actuator has a contacting portion functioning as a guidefor preventing the magnetoelectric transducer 140 from rotating about anaxis of the magnetic field generator 130. The sensor, if being used overa long period of time, has the contacting portion wearing unevenly andcausing backlash, which makes the sensor generate an unstable output.

DISCLOSURE OF THE INVENTION

The present invention addresses the problem discussed above and aims toprovide a position sensor for an electromagnetic actuator. The positionsensor is capable of accurate non-contacting position detection, notrestricting rotation of a shaft to be detected about an axis of theshaft.

To solve this problem, the position sensor of the present inventionincludes: a first magnet being fixed to the shaft to be detected whichmoves axially in synchronization with a movable shaft of theelectromagnetic actuator, and having a first polarity vector parallel tothe axis of the shaft; a second magnet being disposed opposite to thefirst magnet and having a second polarity vector crossing the firstpolarity vector substantially orthogonally three-dimensionally; and amagnetoelectric transducer being disposed over the second magnet andhaving a magnetosensitive axis substantially orthogonal to the first andsecond polarity vectors. The magnetoelectric transducer generates anoutput responsive to an axial movement of the shaft. With thisconfiguration, the position sensor for the electromagnetic actuator candetects the position accurately with no contact, not restricting therotation of the shaft about the axis of the shaft at all.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an electric EGR valve including a positionsensor for an electromagnetic actuator in accordance with an exemplaryembodiment of the present invention.

FIG. 2 is a perspective view illustrating a principle of the positionsensor in accordance with the embodiment.

FIG. 3 is a sectional view illustrating a first magnet fixed to a shaftto be detected in accordance with the embodiment.

FIG. 4 is a cutaway view of an essential part of the position sensor inaccordance with the embodiment.

FIG. 5 illustrates an output characteristic of the position sensor inaccordance with the embodiment.

FIG. 6(a) schematically illustrates a relationship between an operationof the position sensor and an output voltage in accordance with theembodiment, and

FIG. 6(b) schematically illustrates a relationship between the operationof the sensor and an output voltage after a change in temperature.

FIG. 7(a) is a perspective view of a conventional position sensor forthe electromagnetic actuator,

FIG. 7(b) is a cross section taken along an arrow C—C of the sensor, and

FIG. 7(c) is a perspective view detailing a relationship between amagnetoelectric transducer and a magnetic field generator of the sensor.

BEST MODE FOR CARRYING OUT THE INVENTION

(Exemplary Embodiment 1)

FIG. 1 is a sectional view of an electric EGR valve including a positionsensor for an electromagnetic actuator in accordance with the exemplaryembodiment of the present invention. FIG. 2 is a perspective viewillustrating a principle of the position sensor in FIG. 1. FIG. 3 is asectional view illustrating a first magnet fixed to a shaft to bedetected in FIG. 2. FIG. 4 is a cutaway view of an essential part of theposition sensor in FIG. 1.

In FIGS. 1 to 4, reference numeral 1 denotes a shaft to be detectedwhich is shaped like a round bar and is made of non-magnetic stainlesssteel such as austenitic heat-resisting steel (e.g. JIS-listed SUH-31B)or the like. Reference numeral 2 denotes a cylindrical first magnet madeof SmCo rare earth magnet and being attached to the shaft 1 coaxiallywith the shaft 1. Reference numeral 2 a denotes a first polarity vectorindicating a direction of the magnetic polarity of the first magnet 2.Reference numeral 3 denotes a second magnet made of SmCo rare earthmagnet. Reference numeral 3 a denotes a second polarity vectorindicating a direction of magnetic polarity of the second magnet 3.Reference numerals 4 a and 4 b denote first and second magnetic fluxcollecting yokes, respectively. Reference numerals 5 a and 5 b denotefirst and second semiconductor magnetoresistive elements, respectively.Reference numerals 6 a and 6 b denote first and second fixed resistors,respectively. Reference numeral 17 denotes a gold wire. Referencenumeral 18 denotes a molded case. Reference numeral 19 denotes a leadframe. Reference numeral 20 denotes a relay board. Reference numeral 21denotes a relay terminal. Reference numeral 24 denotes a connectorterminal. Reference numeral 25 denotes a connector. Reference numeral 33denotes an armature. Reference numerals 34 denotes a first returnspring. Reference numeral 35 denotes a second return spring. Referencenumeral 36 denotes a first stator. Reference numeral 37 denotes a secondstator. Reference numeral 38 denotes a shaft. Reference numeral 39denotes a valve. Reference numeral 40 denotes an annular coil. Referencenumeral 41 denotes a valve base. Reference numeral 42 denotes arecirculation passage. Reference numeral 43 denotes a valve seat.Reference numeral 44 denotes an inner cover. Reference numeral 45denotes an outer cover. Reference numeral 46 denotes a first bearing.Reference numeral 47 denotes a second bearing. Reference numeral 51denotes an electric EGR valve. Reference numeral 52 denotes a positionsensor. Reference numeral 53 denotes a linear solenoid. Referencenumeral 54 denotes a valve mechanism.

The linear solenoid 53 includes: a vertically-movable armature 33 fitinto an internal cylindrical space formed with respective innerperipheral walls of first and second stators 36, 37 and the coil 40disposed between the lower and upper stators 36, 37; and the firstreturn spring 34 biasing the armature 33 upward. The first bearing 46 isfit into a center of the first stator 36. The shaft 38 is supported bythe bearing 46 to be vertically slidable and movable integrally with thearmature 33 with an upper end of the shaft 38 secured to a center ofarmature 33.

A lower end of the shaft 38 is formed into the valve 39. In the valvebase 41 of the valve mechanism 54, the recirculation passage 42 forexhaust gas is formed. The valve seat 43 is positioned at a midpoint ofpassage 42 within valve base 41, and the valve 39 provided at the lowerend of the shaft 38 is seated on and unseated from the valve seat 43 toselectively close and open.

The shaft 1 supported in vertically movable protrudes into a center ofthe linear solenoid 53 with a lower end of the shaft 1 contacting withthe armature 33.

The second return spring 35 biases the shaft 1 including the firstmagnet 2 mounted thereto downward and is held by the inner cover 44. Theinner cover 44 and an electrical connecting portion between the relayterminal 21 and the connector terminal 24 are covered with the outercover 45.

In FIG. 2, an axis of the shaft 1 is parallel to the first polarityvector 2 a of the first magnet 2. The second magnet 3 is disposedopposite to the first magnet 2. The first and second polarity vectors 2a, 3 a cross to each other substantially at right anglesthree-dimensionally. The first and second magnetic flux collecting yokes4 a, 4 b each made of a magnetic sheet are disposed over opposed sidesof second magnet 3, respectively, and are disposed perpendicularly tothe second polarity vector 3 a of-the second magnet 3. The first andsecond semiconductor magnetoresistive elements 5 a, 5 b are disposedover respective sides of the yokes 4 a, 4 b. A magnetosensitive axis ofthe first and second magnetoresistive elements 5 a, 5 b is orthogonal tothe first and second polarity vectors 2 a, 3 a. The first and secondmagnetoresistive elements 5 a, 5 b and first and second fixed resistors6 a, 6 b are electrically connected to form a Wheatstone bridge.

Regarding dimensions of the essential parts shown in FIG. 2, the secondmagnet 3 has a length along the second polarity vector 3 a of 4 mm, alength in parallel with the shaft 1 of 5 mm, and a length perpendicularto the shaft 1 of 4 mm. Each of the first and second yokes 4 a, 4 b hasa thickness of 10 mm. The first magnet 2 has an outside diameter of φ8mm and an axial length of 12 mm. The distance between an outerperipheral surface of the first magnet 2 and a surface of the firstmagnetoresistive element 5 a as well as the distance between the outerperipheral surface of the first magnet 2 and a surface of the secondmagnetoresistive element 5 b is 2.8 mm.

In FIG. 3, the first magnet 2 is made of resin paste including the SmCorare earth magnet and is insert-molded into a pipe 1 a. A projection 1 bprovided at the pipe 1 a prevents the pipe from getting out. The pipe 1a is press-fit to the shaft 1.

In FIG. 4, the first and second semiconductor magnetoresistive elements5 a, 5 b are die-bonded to the lead frame 19, and electrodes (not shown)disposed over magentoresistive elements 5 a, 5 b are wire-bonded to thelead frame 19 by a gold wire 17. These components are subjected totransfer molding, so that molded case 18 is formed over the first andsecond magnetic flux collecting yokes 4 a, 4 b and the second magnet 3.The lead frame 19 is electrically coupled to the relay terminal 21 viathe relay board 20. These components are covered with a sealing resin22. As shown in FIG. 1, the relay terminal 21 is electrically connectedto the connector terminal 24, and connector 25 outputs a signal.

An operation in accordance with the present embodiment will behereinafter described.

In the electric EGR valve 51, a current input from a control ECU (notshown) to the coil 40 varies, the shaft 38 moves accordingly.Consequently, an opening of the valve 39 as well as an amount of exhaustgas recirculated varies accordingly. Simultaneously, the moving shaft 38moves the shaft 1 of the position sensor 52, and the first magnet 2mounted to the shaft 1 moves accordingly. This changes a strength of amagnetic field applied to the first and second magnetoresistive elements5 a, 5 b disposed over the respective sides of the yokes 4 a, 4 bdisposed over the respective opposed sides of the second magnet 3perpendicularly to the second polarity vector 3 a of the second magnet 3opposite to the first magnet 2. The variance of the magnetic fieldstrength get respective resistances of the magnetoresistive elements 5a, 5 b to vary. The Wheatstone bridge formed with the first and secondmagnetoresisitive elements 5 a, 5 b and the first and second fixedresistors 6 a, 6 b converts the resistance changes into a change involtage.

FIG. 5 illustrates an output of the position sensor 52 described inabove. The horizontal axis of FIG. 5 represents a displacement of thefirst magnet 2 about a reference center of the second magnet 3 in aparallel direction with the shaft 1 of the second magnet 3, and thevertical axis represents an output voltage of the position sensor 52.The output voltage varies linearly with the displacement of the firstmagnet 2. When the displacement changes from −5 mm to +5 mm, the outputvoltages ranges in a large value, 1V or more.

The moving amount of the shaft 38 corresponds to the opening of thevalve 39, and the detected opening is fed back to the ECU for control.The movement of the shaft 38 is restricted by the armature 33 includingthe shaft 38 secured thereto, and the first and second bearings 46, 47.In other words, the valve 39 is located at a fully-closing position(corresponding to a displacement of +4 mm in FIG. 5) when the armature33 contacts with the bearing 47, and is located at a fully-openingposition (corresponds to a displacement of −4 mm in FIG. 5) when thearmature 33 contacts with the bearing 46.

A relationship between such operating pattern and the output voltage isshown schematically in FIG. 6(a). In FIG. 6(a), reference symbol Vcdenotes an output voltage (corresponding to 3.0V in FIG. 5) representingthe fully-closing position, reference symbol Vo denotes an outputvoltage (corresponding to 2.0V in FIG. 5) representing the fully-openingposition, and reference symbol V denotes the present output voltage.

A present actual valve position X based on FIG. 6(a) can be expressedas:$X = \frac{\left( {V - {V\quad o}} \right) \times 1s\quad t\quad r\quad o\quad k\quad e}{{V\quad c} - {V\quad o}}$

With the above-mentioned configuration, a temperature drift of theoutput voltage resulting from a temperature change occurs as shown inFIG. 6(b). In FIG. 6(b), reference symbol Vc1 denotes an output voltagerepresenting the fully-closing position after the temperature drift,reference symbol Vo1 denotes an output voltage representing thefully-opening position after the temperature drift, and reference symbolV1 denotes the present output voltage after the temperature drift.

Even if the temperature changes, the present actual valve position X canbe obtained by the equation:$X = \frac{\left( {{V1} - {V\quad {o1}}} \right) \times 1s\quad t\quad r\quad o\quad k\quad e}{{V\quad {c1}} - {V\quad {o1}}}$

In the present embodiment, the first and second magnets 2, 3 and thefirst and second magnetic flux collecting yokes 4 a, 4 b basically forma substantially-closed magnetic circuit hardly affected by an externalmagnetic field.

In this embodiment, the distance between the outer peripheral surface ofthe first magnet 2 and the surface of the first semiconductormagnetoresistive element 5 a as well as a distance between the outerperipheral surface of the first magnet 2 and the surface of the secondsemiconductor magnetoresistive element 5 b is 2.8 mm. However, thedistance ranging from 2.5 mm to 3.1 mm ensures the same effect.

In this embodiment, the position sensor 52 is provided independentlyupon the linear solenoid 53 and valve mechanism 54. This facilitatesreplacing the position sensor 52 having an problem even during beingmanufactured. Also, even if the shaft 1 rotates about its axis, thesensor detects the position accurately. This is because the first magnet2 is cylindrical and coaxial with the shaft 1, and the space between thefirst and second magnetoresistive elements 5 a, 5 b remains invariable.Further, the sensor detects the position accurately since the first andsecond magnets 2, 3 employs the SmCo rare earth magnet hardly having amagnetic force hardly changing due to the temperature change or due to adecline of durability.

According to the present embodiment, an amplifier for the output of theposition sensor 52 is not employed. However, the output may come outthrough the amplifier. This is applicable to cases where a processor inthe subsequent stage requires a signal voltage reaching a specified orhigher input level. The amplifier may be an AC amplifier. The ACamplifier is applicable to detecting the position of the shaft 1 movingat a specified or higher frequency. Thus, the system has an advantagethat the temperature drift affecting the first and second semiconductormagnetoresistive elements 5 a, 5 b can be cancelled for more accuratedetection.

A bare chip, functioning as the amplifier, and the first and secondsemiconductor magnetoresistive elements 5 a, 5 b may be packaged intoone by being die-bonded to the lead frame 19 and wire-bonded by a goldwire 17. Consequently, the wiring between the first and secondmagnetoresistive elements 5 a, 5 b and the bare chip is reduced, thusimproving noise immunity. In addition, a circuit board can have areduced area since requiring little external circuitry, thus allowingthe sensor to be small.

In the present embodiment, the electric EGR valve to which the positionsensor is applied is described. However, the position sensor of thepresent invention is applicable to various devices each including asolenoid-valve-driving device and the like employing an electromagneticactuator.

In the solenoid-valve-driving device, the valve and the valve seat weardue to a repeated use over a long period of time, so that the seatingposition of the fully-closing valve changes. Even in this case, thedevice, upon monitoring the output voltage of the position sensor at thefully-closing position, utilizing the voltage as information useful fordiagnosis.

In the present embodiment, the semiconductor magnetoresistive elementsis used as a magnetoelectric transducer, but the magnetoelectrictransducer is not limited to it, and may employ, for example, a Hallelement.

In this embodiment, the magnetic flux collecting yokes 4 a, 4 b eachmade of a sheet made of the magnetic material are disposed over therespective opposed sides of the second magnet 3 and disposedperpendicularly to the second polarity vector 3 a. The first and secondsemiconductor magnetoresistive elements 5 a, 5 b is disposed over therespective sides of the yokes 4 a, 4 b with the magnetosensitive axis ofthe elements 5 a, 5 b substantially orthogonal to the first and secondpolarity vectors 2 a, 3 a. However, the present invention is not limitedto this example. For example, the first and second semiconductormagnetoresistive elements 5 a, 5 b functioning as the magnetoelectrictransducer may be disposed over the second magnet 3 with respectivemagnetosensitive axis thereof substantially orthogonal to the first andsecond polarity vectors 2 a, 3 a. In this case, it is preferable thateach of first and second magnetoresistive elements 5 a, 5 b is disposedover an end of the second magnet 3 for its output sensitivity.

INDUSTRIAL APPLICABILITY

According to the present invention, as explained above, a positionsensor for an electromagnetic actuator detects a position accuratelywith no contact, while not restricting the rotation of a shaft thereofto be detected about the axis of the shaft at all.

Reference Numerals 1 Shaft To Be Detected 1a Pipe 1b Projection 2 FirstMagnet 2a First Polarity Vector 3 Second Magnet 3a Second PolarityVector 4a First Magnetic Flux Collecting Yoke 4b Second Magnetic FluxCollecting Yoke 5a First Semiconductor Magnetoresistive Element 5bSecond Semiconductor Magnetoresistive Element 6a First Resistor 6bSecond Resistor 17 Gold Wire 18 Molded Case 19 Lead Frame 20 Relay Board21 Relay Terminal 24 Connector Terminal 25 Connector 33 Armature 34First Return Spring 35 Second Return Spring 36 First Stator 37 SecondStator 38 Shaft 39 Valve 40 Coil 41 Valve Base 42 Recirculation Passage43 Valve Seat 44 Inner Cover 45 Outer Cover 46 First Bearing 47 SecondBearing 51 Electric EGR Valve 52 Position Sensor 53 Linear Solenoid 54Valve Mechanism

What is claimed is:
 1. A position sensor for an electromagneticactuator, comprising: a shaft to be detected moving axially insynchronization with a movable shaft of the electromagnetic actuator; afirst magnet fixed to said shaft, said first magnet having a firstpolarity vector parallel with an axis of said shaft; a second magnetdisposed opposite to said first magnet, said second magnet having asecond polarity vector substantially orthogonal to said first polarityvector; and a magnetoelectric transducer disposed between said first andsecond magnets, said magnetoelectric transducer having amagnetosensitive axis substantially orthogonal to said first and secondpolarity vectors; wherein said magnetoelectric transducer generates anoutput responsive to an axial movement of said shaft.
 2. The positionsensor of claim 1, wherein said first magnet is cylindrical and coaxialwith said axis of said shaft to be detected.
 3. The position sensor ofclaim 1, wherein said magnetoelectric transducer includes first andsecond semiconductor magnetoresistive elements disposed over said secondmagnet and aligned in parallel with said second polarity vector.
 4. Theposition sensor of claim 3, further comprising an amplifier providedbetween said first and second semiconductor magnetoresistive elements.5. The position sensor of claim 1, wherein each of said first and secondmagnets made of SmCo rare earth magnet.
 6. The position sensor of claim1, wherein said shaft to be detected is made of non-magnetic material.7. A position sensor for an electromagnetic actuator, comprising: ashaft to be detected moving axially in synchronization with a movableshaft of the electromagnetic actuator; a first magnet fixed to saidshaft, said first magnet having a first polarity vector parallel with anaxis of said shaft; a second magnet disposed opposite to said firstmagnet, said second magnet having a second polarity vector substantiallyorthogonal to said first polarity vector; two magnetic flux collectingyokes disposed on respective opposed sides of said second magnet anddisposed perpendicularly to said second polarity vector, said magneticflux collecting yokes being made of magnetic material; andmagnetoelectric transducers disposed at respective sides of saidmagnetic flux collecting yokes and between said first and secondmagnets, said magnetoelectric transducers each having a magnetosensitiveaxis substantially orthogonal to said first and second polarity vectors,wherein said magnetoelectric transducers generate outputs responsive toan axial movement of said shaft.
 8. The position sensor of claim 7,wherein said magnetoelectric transducers include first and secondsemiconductor magnetoresistive elements disposed over said respectivesides of said magnetic flux collecting yokes, said first and secondsemiconductor magnetoresistive elements being aligned in parallel withsaid second polarity vector.